Not really sure why people are debating this at all, the only feasible option is to make it so kicked players can't re-enter the group they were kicked from. The solution is simple so why are you guys trying to complicate it?

Odds are it wasn't SE's intention for kicked players to re-enter the same dungeon and it only really applies to jobs in short demand. I'm willing to bet that this QoL change is on their list and that they just haven't gotten to it yet.

Out of all my time playing this game I've only encountered this issue one time so I wouldn't call it a high priority based on my own personal experience but I would like to see the change made. If your friend is going to quit over one bad experience then he's probably going to quit anyways, tell him to get over it and move on.